The vogue thing to do on the internet is to insist that you see a doctor. Too bad TK doesn't seem to post in here anymore or maybe he could give you a "decent" differential diagnosis. I'm not saying it's actually your thyroid, however the majority of thyroid nodules are benign and while a painful lump on a thyroid sounds bad, but there are benign painful thyroid lumps. You should probably get it looked at.

Should not typically stretch out with elastane. This isn't entirely true and women do complain that their elastane denim bags out over time. Guy tend not to wear theirs quite so tight.
Lighter denims do not typically fade. A raw, light colored denim may exhibit some fading eventually. There is no significant benefit of a raw, light denim over a light denim.